Multiple days selection using addRange method

[takumade]

Hi This is more of a cosmetic feature

I ve added addRange method which allows you to select multiple days without calling the add method multiple times.

So Instead of doing this to select multiple days programmatically:

MultipleMarkedDates multipleMarkedDates = new MultipleMarkedDates(markedDates: []);
multipleMarkedDates.add(new MarkedDate(date: DateTime(2021, 7, 12), color: Colors.purple));
multipleMarkedDates.add(new MarkedDate(date: DateTime(2021, 7, 13), color: Colors.purple));
multipleMarkedDates.add(new MarkedDate(date: DateTime(2021, 7, 14), color: Colors.purple));

They can now do this instead:

MultipleMarkedDates multipleMarkedDates = new MultipleMarkedDates(markedDates: []);
multipleMarkedDates.addRange(new MarkedDate(date: DateTime(2021, 8, 4), color: Colors.purple), plus: 5);

This will select the following days

2021 / 8 / 4
2021 / 8 / 5
2021 / 8 / 6
2021 / 8 / 7
2021 / 8 / 8
2021 / 8 / 9

addRange Method

addRange methods accepts the following arguments

Argument	Type	Description	Required	Default
date	MarkedDate	Specify which date will be selected	Yes
plus	int	The number of days to select after date	No	0
minus	int	The number of days to select before date	No	0

FAQ
1. Did you remove the add method?
No

2. What if a user leaves plus and minus arguments?
It will just select date only

[hyochan]

LGTM!